Hoist for lift trucks

ABSTRACT

Hoist of the high free-lift type with three pairs of masts, for lift trucks, comprising a plate carrying forks slidable in the guides of the innermost pair of masts, the latter being slidable in the guides of the pair of movable intermediate masts sliding in turn in the grooves of the pair of fixed masts, a telescopic cylinder with two pistons, namely a smaller and a larger piston, mechanical transmission means adapted to transmit the movements from the cylinder to the plate and thereafter to the movable masts, and abutment means for carrying the pair of intermediate masts along, in which the smaller piston is connected to the plate to obtain, with respect to the cylinder, movements of the plate twice those of said smaller piston, and the larger piston is connected to the pair of fixed masts to obtain movements of the cylinder with respect to the fixed masts three times those of the larger piston with respect to the cylinder itself, the thrust area of the larger piston being practically one and a half times the thrust area of the smaller piston.

United States Patent Pittaluga [4 1 Mar. 28, 1972 [54] HOIST FOR LIFT TRUCKS Primary Examiner-Harvey C. Homsby [72] Inventor. Gennaro Pittaluga, Milan, Italy Atwmey Stevens"Davis Miner & Mosh [73] Assignee: Fiat Soc. per Azioni Azienda 0M Stabilimento di Milano, Milan, Italy ABSTRACT [22] Filed: Oct. 17, 1969 Hoist of the high free-lift type with three pairs of masts, for lift Appl. No.: 867,332

Foreign Application Priority Data trucks, comprising a plate carrying forks slidable in the guides of the innermost pair of masts, the latter being slidable in the guides of the pair of movable intermediate masts sliding in turn in the grooves of the pair of fixed masts, a telescopic cylinder with two pistons, namely a smaller and a larger piston, mechanical transmission means adapted to transmit the movements from the cylinder to the plate and thereafter to the movable masts, and abutment means for carrying the pair of inten'nediate masts along, in which the smaller piston is connected to the plate to obtain, with respect to the cylinder, movements of the plate twice those of said smaller piston, and the larger piston is connected to the pair of fixed masts to obtain movements of the cylinder with respect to the fixed masts three times those of the larger piston with respect to the cylinder itself, the thrust area of the larger piston being practically one and a half times the thrust area of the smaller piston.

1 Claim, 6 Drawing Figures P'ATENTED MR 2 8 1972 SHEET 1 UF 4 a w m 9 h ////X//X/XA/ lnoenlor GENNARQ PITTALUGA PATENTEU MAR 2 a 1972 SHEET 2 UF 4 lnvenlor GENNARQ PITTALUGA B MM JW PATENTEIJMAW I912 3,651,891

SHEET [1F 4 Inventor GEN NARO PITTALUGA B JMQW A ltorneys HOIST FOR LIFT TRUCKS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hoist for lift trucks belonging -to the class of hoists constituted by three pairs of masts, two of them movable and one fixed, which are fitted one within the other with the possibility of sliding, a plate slidable in turn along the innermost pair of masts and carrying forks and/or special fixtures employed for moving various objects, and at least one hydraulic cylinder which raises the plate and masts through mechanical transmission means, such as, for example, rollers and chains and other means, and more precisely, in a first stage, called free lift, raises the plate to the maximum height without the pairs of movable masts moving and without the cylinder itself projecting beyond the minimum overall height defined by the masts themselves in the retracted position, while in a second stage the cylinder produces with the same mechanical transmission means which take part in the free lift, or with others different to the latter, the raising of the movable masts together with the plate until the maximum elevation of said plate is obtained.

These hoists or elevating mechanisms find special use in all those cases in which shifting of the load involving transfers from high places to low places and vice versa is required, just as happens, for example, in the case of the loading or unloading of containers for transport purposes (so-called containers) by means of lift trucks.

2. Description of the Prior Art According to the current art, these hoists which, as has already been said, have as their fundamental characteristic that of permitting the maximum elevation of the plate and, consequently, of the load supported thereby through the medium of the forks or other equipment without any variation in the minimum overall height of the hoist with the masts retracted, may be of the type having a plurality of single cylinders or a single telescopic cylinder.

While the multi-cylinder type has the advantage of having the raising speed of the plate during the free lift equal to that of the plate during the raising of the movable masts, it presents the disadvantage of having a plurality of cylinders of which at least one is of a height practically equal to that of the hoist when closed, which reduces visibility for the driver in the stage of translation of the truck.

The type having a single telescopic cylinder, in turn, may be equipped with a high cylinder or a low cylinder, there being meant bya high cylinder one with a height practically equal to that of the hoist when closed and by a low cylinder one with a height less than that of the hoist when closed. In the first case, as has already been said in connection with the multi-cylinder hoists, the speed of the plate does not undergo variations during the shifting thereof, but visibility is reduced for the driver; in the second case, that is where the hoist has a low cylinder, there is good visibility.

Finally, hoists with a low telescopic cylinder are further more divided into hoists in which the speed of the plate during the free lift is different to that during the raising of the movable masts and hoists in which the speed remains the same in the two stages.

SUMMARY OF THE INVENTION The present invention relates to a hoist of the last type, that is a hoist with a low telescopic cylinder which allows good visibility and having a constant speed of the plate, with consequent elimination of jerking or jolting of the load in the stage of transition from free lift to elevation with the masts in motion.

This hoist is characterized substantially in that the smaller piston is connected kinematically to the plate slidable along the guides of the pair of innermost masts through mechanical transmission means such as to obtain, with respect to the cylinder, movements of the plate (free lift) twice those of said smaller piston, and that the larger piston is connected kinematically to the pair of fixed masts through mechanical transmission means separate from those of the smaller piston and such as to obtain movements of the cylinder with respect to the fixed masts three times those of the larger piston with respect to the cylinder itself, the thrust area of the larger piston being practically one and a half times that of the thrust area of the smaller piston.

BRIEF DESCRIPTION OF THE DRAWINGS Purely by way of example and without any restrictions, there will now be described a diagrammatic constructional form and a practical embodiment of the hoist according the invention. In the accompanying drawings, to which this description refers:

FIGS. 1, 2 and 3 show respectively from the side, in diagrammatic form, the hoist fully lowered, the hoist with the forks at maximum free lift and the hoist with the forks at maximum elevation, while FIGS. 4 and 5 are two front views of a practical embodiment of the same hoist mounted on a lift truck, the hoist being fully lowered and at maximum elevation, respectively; and

FIG. 6 is a side view of the hoist of FIGS. 4 and 5 partly in section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the reference 1 indicates the hydraulic cylinder equipped with two plunging pistons 2, 3 fitted one within the other and both contained in the cylinder.

The piston 2 of larger diameter is inserted at the bottom, while the piston 3 of smaller diameter is inserted at the top. The cylinder 1 is fixed to the inner pair of movable masts 4.

The ratio between the thrust areas of the two pistons is 1.5

The cap or head 5 of the smaller piston 3 is equipped with one or more pulleys 6 on which are placed the chains 7 which are anchored at one end to the cylinder 1 and support at the other end the plate with the forks 8, which move at a speed twice that of said piston 3 (FIG. 2).

The head or cap 9 of the piston 2 of larger diameter is equipped with pulleys 10 and anchorages 11 cooperating by means of other chains 12 separate from the first-mentioned chains with other pulleys 13 mounted towards the bottom of the cylinder. The last-mentioned chains are anchored to the upper end of the fixed masts 14, then passed at the bottom round the pulleys 10 at the head of the piston in the grooves of said pulleys and over half the circumference thereof and ascend and pass at the top round the pulleys 13 (mounted towards the bottom of the cylinder) in the grooves of said pulleys and over half the circumference thereof, being finally fixed by their ends to the anchorages 11 with which the head 9 is provided.

Under these conditions, the larger piston 2 (FIG. 3) produces the movement of the cylinder 1 (and therefore of the pair of innermost masts 4 to which the cylinder itself is fixed) at a speed three times that of said piston.

Bearing in mind that the larger piston 2 has 5 thrust section 1.5 times greater than that of the smaller piston 3, with equality of the flow of oil feeding the cylinder the speed of the forks 8 in free lift is equal to that of the pair of innermost masts 4.

Irrespective of the load on the forks, the raising action begins with the plate and forks 8 slidable along the innermost masts 4 by the action of the upwardly directed piston 3, while the pairs of movable masts 4 and 15 remain stationary until such time as the plate engages with the upper part of the innermost masts 4 at 16.

In this way the free lift is performed and, consequently, the stroke of the piston 3. From this instant, the pressure in the cylinder increases owing to the effect of the dead weight of the cylinder 1 with the lower piston 2 and cap 9, the weight of the inner movable masts 4 and, thereafter, the weight of the intermediate masts 15 and produces the displacement of the larger piston 2 with respect to the cylinder 1 and, therefore, the lifting of the inner masts 4 together with that of the forks 8.

In a given position in the course of the raising action, the projections 17 forming part of the cap 9 of the larger piston 2 (or forming part, in a suitable position, of the inner movable masts) engage abutments 18 located on the movable intermediate masts 15, thus producing the raising of the latter.

in the descent stage, the movable masts will be lowered first and, only when these have completed their travel, will it be possible for the plate and the forks 8 to be lowered along the innermost masts.

It is understood that other practical embodiments may be different from that which has just been described without departing thereby from the scope of the invention.

Iclaim:

l. A hoist, comprising, in combination:

a first pair of fixed masts;

second and third pairs of masts movable with respect to each other and to said first pair of masts;

a load-carrying plate slidably connected to said third pair of I masts;

a single cylinder arrangement carried by said third pair of masts;

first and second telescoping piston members movably extending from said cylinder inopposite direction, wherein the thrust area of one of said first and second piston members is one and one-half times the thrust area of the other of said first and second piston members; and wherein the movement of said load-carrying plate with respect to said cylinder is approximately twice as great as the movement of said second piston with respect to said cylinder;

a first pulley mounted on said first piston member;

a second pulley;

means connecting said second pulley to said cylinder;

first and second flexible means;

means connecting one end portion of said first flexible means to at least one of said first masts;

means connecting a second end portion of said first flexible means to said first piston member;

said first flexible means being trained at least partially around said first and second pulleys;

a third pulley mounted on said second piston member;

means rigidly connecting one end portion of said second flexible means to said cylinder; and

means connecting a second end portion of said second flexible means to said load-carrying plate;

said second flexible means being trained at least partially around said third pulley. 

1. A hoist, comprising, in combination: a first pair of fixed masts; second and third pairs of masts movable with respect to each other and to said first pair of masts; a load-carrying plate slidably connected to said third pair of masts; a single cylinder arrangement carried by said third pair of masts; first and second telescoping piston members movably extending from said cylinder in opposite direction, wherein the thrust area of one of said first and second piston members is one and one-half times the thrust area of the other of said first and second piston members; and wherein the movement of said loadcarrying plate with respect to said cylinder is approximately twice as great as the movement of said second piston with respect to said cylinder; a first pulley mounted on said first piston member; a second pulley; means connecting said second pulley to said cylinder; first and second flexible means; means connecting one end portion of said first flexible means to at least one of said first masts; means connecting a second end portion of said first flexible means to said first piston member; said first flexible means being trained at least partially around said first and second pulleys; a third pulley mounted on said second piston member; means rigidly connecting one end portion of said second flexible means to said cylinder; and means connecting a second end portion of said second flexible means to said load-carrying plate; said second flexible means being trained at least partially around said third pulley. 